Of course, if you use different values for axes or extruders then you need two lines. e.g.

M350 X16 Y16 Z16 I1; set micro stepping for X,Y and Z to 16X with interpolation
M350 E32; set micro stepping for extruders to 32X

Adding the comments makes life a lot easier when you want to change something a few months or years later. Also, and no disrespect to David, but "fat finger syndrome" can affect us all, so explicitly setting values for parameters that have default values will make things safer in the event of said "fat finger syndrome" striking while David is tweaking the firmware.